The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft engine, which is generally of the turbojet engine type, is placed inside a nacelle, which, among other functions:                provides the aerodynamic fairing of the engine,        makes it possible to channel the outer air towards the engine,        makes it possible to connect the engine to the aircraft.        
In fact, the nacelle generally, exhibits a tubular structure comprising an air inlet upstream of the turbojet engine, a median section intended to surround a fan of the turbojet engine, a downstream section intended to surround the combustion chamber of the turbojet engine and optionally housing, thrust reversal means.
Modern nacelles are intended to house a dual flow turbojet engine able to generate by means of vanes of the fan in rotation a hot air flow (also called main exhaust flow) coming from the combustion chamber of the turbojet engine and a cold air flow (bypass air) which circulates outside the turbojet engine through an annular passage, also called stream, formed between a fairing of the turbojet engine and an inner wall of the nacelle. The two air flows are ejected from the turbojet engine via the rear of the nacelle.
The downstream section of a nacelle for such a turbojet engine generally exhibits, a fixed outer structure, called Outer Fixed Structure (OFS) and a fixed inner structure, called Inner Fixed Structure (IFS), surrounding a downstream section of the turbojet engine housing the gas generator of the turbojet engine.
The inner and outer fixed structures define the stream intended to channel the cold air flow which circulates outside the turbojet engine.
In a particular case of a grid-type thrust reversal device, the means implemented for reorienting the cold air flow comprise grids for deviating the cold air flow and a mobile cowl moveable between, on the one hand a deployed position in which it opens in the nacelle a passage intended for the deviated cold air flow, and on the other hand, a retractable position in which it closes this passage, the cowl merely having a sliding function aiming to uncover or recover these grids.
Typically, this thrust reversal device comprises two semi-cylindrical half-cowls, mounted in such a manner as to be able, particularly during maintenance work, to be opened “butterfly” by swiveling around a longitudinal hinge line, next to a suspension pylon by which the nacelle is connected to the wing or fuselage of the aircraft. Such a structure is called a C-duct.
The IFS can also be formed of a C-duct structure and be unfolded “butterfly” by swiveling around a longitudinal hinge line, next to the suspension pylon between an operating position and a maintenance position with a view to providing access to the gas generator during maintenance work.
According to an alternative form of the nacelle, a portion of the IFS and the half-cowls must be able to open at the same time in “butterfly”, during maintenance work.
Each of the two half-cowls is, hence, slidingly mounted on a longitudinal half-beam support, so-called 12 o'clock beam, pivotally mounted on the pylon, the rotation movement of each half-beam on the pylon providing the swiveling of each half-cowl with respect to this pylon.
Thus, typically, in order to provide these particular movements of the cowl and make possible the fastening of the half-cowls, each half-beam will be provided with rails intended to cooperate with guides mounted on the half-cowls to provide the translation of the related half-cowl and of a plurality of hinge clevises capable of allowing the articulation of the half-beam on the associated pylon.
During maintenance work on the ground, the C-duct type structures have the advantage of providing easy access to the engine after unlocking the holding systems of the half-cowls then swiveling of the latter.
However, although meeting the need of a rapid and easy access to the engine, such a configuration of mounting of the rear nacelle assembly on the pylon has the drawback of significantly weighing down the nacelle as well as having an important size.
Another drawback is the simultaneous opening of the IFS and the cowl which requires the IFS and the cowl to be directly connected together at the top portion of the cowl.
This connection requires the presence of suitable fastening structures which weigh down the nacelle just as much and complicate its assembling.
Nacelles exhibiting other configurations have been developed and particularly O-Duct type nacelles, which have a substantially peripheral cowl and an almost annular shape.
In such a configuration, in operation or during maintenance work, the opening of the cowl can be carried out by sliding along the guiding rails able to be preserved on either side of the suspension pylon, the supporting beams present at a 12 o'clock position and a 6 o'clock position in the C-duct structures which may hence be removed.
In this type of nacelle structure, at least one portion of the inner structure can, itself also be sliding or swiveling along the axis parallel to the sliding axis of the cowl, during maintenance work.
Maintenance of such a configuration is tricky: there is the risk of the cowl getting jammed during its movement.
Furthermore, the access to the rear portion of the engine may be tricky due to the limitation of the sliding towards the rear of the inner structure linked the geometry of the nacelle.
Moreover, such a nacelle structure provides great flexibility to the nacelle, making it more prone to deformation.